A solar cell using an organic material has been highlighted due to the advantages of easy processability, diversity, low fabricating costs, and high flexibility, and is rapidly growing along with the development of a new material.
An organic semiconductor has been forecast to emerge as an essential material in the fabrication of an inexpensive solar cell, such as a thin film-type device, a large area device, and a flexible device which may be applied by a roll-to-roll method, based on low costs and easiness in fabrication process, which are the largest advantages of an organic material.
The possibility of an organic solar cell was first proposed in the 1970s, but the efficiency thereof was so low that no practical use was found.
However, in 1986, C. W. Tang at Eastman Kodak Company showed the possibility of commercialization into various solar cells from a two-layer structure using copper phthalocyanine (CuPc) and a perylene tetracarboxylic acid derivative, and as a result, great development has been brought while interests in and researches for the organic solar cell have been rapidly increased.
Thereafter, as a concept of bulk heterojunction (BHJ) was introduced by Yu, et al., in 1995, and a fullerene derivative with enhanced solubility, such as PCBM was developed as an n-type semiconductor material, a breakthrough has been achieved in terms of efficiency of the organic solar cell.
However, problems in that a starting material fullerene is expensive and difficult to synthesize, the solubility thereof is not good, and the like are still a big obstacle to the development of an e-donor material.
In order to replace the existing material, studies have been continuously conducted on the development of e-donor materials having low bandgap and new e-acceptor materials having good charge mobility.